Computers are being applied increasingly to uses outside of an office, for example, for notebook computers, portable digital devices, and point-of-sale transaction processing. Accordingly, it is desirable to make printers smaller, lighter, and more functional so that printed documents can be conveniently obtained from printers accompanying such external uses.
For some types of point-of-sale transaction processing, a document and a copy must be made at the same time, for example, for credit card transactions where an original of a charge slip is retained by the vendor and a copy is provided to the purchaser. Such document copies are conventionally obtained by using impact printers and paper with a carbon copy sheet supplied in tandem. Such carbon copies can become messy with spurious impressions, and impact printers are noisy and provide a low-grade image compared to other types of printers. On the other hand, laser printers require a laser imaging engine which is rather bulky and heavy and are therefore not convenient for portable or point-of-sale uses. Inkjet printers are quiet and lightweight but are comparatively slow.